1. Field of the Invention
The present invention generally relates to an alarm apparatus for a motor vehicle for issuing an alarm upon detection of an obstacle (e.g. another motor vehicle) existing laterally rearward of a traveling motor vehicle. More particularly, the present invention is concerned with an alarm apparatus for a motor vehicle which is capable of preventing generation of an erroneous alarm due to detection of a stationary object such as a guardrail without incurring any appreciable increase in the cost.
2. Related Art
Heretofore, there has been proposed an alarm apparatus for a motor vehicle for detecting an obstacle existing in the vicinity of the motor vehicle by means of a range-finding sensor or the like for issuing a relevant message to a driver in the course of traveling with a view to evading accidents or mishaps.
Some of the alarm apparatuses of the type mentioned above are so arranged as to generate an alarm when a succeeding motor vehicle existing in the lane changing direction of a motor vehicle traveling ahead (hereinafter referred to as the own motor vehicle only for the convenience of description) for thereby detecting imprudent overtaking of the succeeding motor vehicle by making decision as to whether or not the succeeding motor vehicle exists obliquely rearward of the own motor vehicle as viewed in the lane changing direction thereof.
More specifically, lane change indicating manipulation (operation of a turn indicator) is detected, and then decision is made as to whether or not a succeeding motor vehicle had entered a predetermined range at the time point when the turn indicator was put into operation, whereon an alarm messaging possibility of the succeeding motor vehicle passing ahead is issued in dependence on the result of the above decision. For particulars, reference may have to be made to Japanese Patent Application Laid-Open No. 118036/1979 (FIGS. 1 to 3).
Further, in the hitherto known alarm apparatus of another type, the vehicle traveling situation is discriminatively identified on the basis of outputs of a steering angle sensor and a yaw rate sensor or navigation information to detect an object of concern existing in the direction determined from the vehicle traveling situation. When an obstacle is detected in a space surrounding the motor vehicle, then an alarm is issued. For particulars, reference may have to be made to Japanese Patent Application Laid-Open No. 233699/2000 (FIGS. 1 to 6).
In the conventional alarm apparatus for the motor vehicle such as disclosed in Japanese Patent Application Laid-Open No. 118036/1979, alarm messaging the existence of an obstacle rearward of the motor vehicle is issued on the basis of the output of the range-finding sensor only. Consequently, the alarm will be issued for all the objects which have entered a certain predetermined range. By way of example, the alarm will unnecessarily or undesirably be issued in response to detection of a stationary object (e.g. guardrail, barrier or the like) in addition to the succeeding motor vehicle, giving rise to a problem that erroneous alarms are likely to be frequently generated to uncomfortableness of the driver of the motor vehicle.
Of course, in the alarm apparatus disclosed in Japanese Patent Application Laid-Open No. 118036/1979 such measures are adopted for suppressing generation of the erroneous alarm by discriminatively identifying the vehicle traveling situation with the aim to enhance the accuracy of alarm generation. To this end, however, expensive instruments such as the yaw rate sensor and the navigation system are required as the information acquiring means for detecting the stationary object, incurring increase of the cost.